This post originally appeared on FoxNews.com, and was written in coordination with Michelle Nunn, Carolyn Woo, Neal Keny-Guyer, Raymond C. Offenheiser, & Richard Stearns.

More than 4 million Syrian refugees, almost half of whom are children, have fled unspeakable violence. Even with winter advancing, many continue to make the treacherous journey from Turkey to Greece by boat, and many, like Aylan Kurdi, the little boy prostrate on the beach whose image sparked renewed dialogue on the crisis, have perished.

The attacks in Beirut and Paris were horrific and a terrifying window into the daily lives of the millions of Syrians that remain inside Syria.

The United States has a long, proud history of aiding persecuted people. Instead of turning Syrian refugees away, we must both assist those who remain in the Middle East and provide safe haven for those who feel compelled to leave.

Unfortunately, some of our leaders have proclaimed that desperate Syrians fleeing for their lives are unwelcome in the United States. Public concern is an understandable response to recent events and the security screening process should be regularly reviewed to ensure that it is effective and efficient.

To be American is to be generous and compassionate. We should not close the door on all Syrian refugees in this, their darkest hour.

Terrorist threats to the United States are real and the U.S. government has a responsibility to keep the public safe. It is important though for everyone to remember that refugees themselves are fleeing violence and are subject to the greatest number of security checks of anyone coming to the U.S. The process can take two years or even longer due to required screenings, in-person interviews, investigations, and clearance by a host of government agencies including the Department of State, Department of Homeland Security, FBI, National Counterterrorism Center and U.S. and international intelligence agencies.

As leaders of the largest humanitarian organizations based in the U.S., we are proud to represent the most charitable nation in the world. To be American is to be generous and compassionate. We should not close the door on all Syrian refugees in this, their darkest hour.

Even as we admit more Syrian refugees, our response must target the root causes of the Syrian exodus. The U.S. has been the most generous donor to humanitarian relief efforts aimed at supporting the Syrian people and neighboring countries. And yet, more must be done. The U.S. and other countries influential in the region must redouble their efforts to find a political solution to the war hand in hand with the Syrian people, do more to protect civilians, ensure humanitarian access to those in need inside Syria, and provide urgently needed financial support to Syria’s neighbors who are shouldering the burden of hosting more than 4 million refugees.

As the violence of the Syrian conflict spills out beyond its borders now is the time to act with compassion, not fear.